This invention relates generally to thermal probes or catheters and more particularly to probes or catheters having a) a heat transmitting core (e.g. a core comprising a heated element, a lumen for transmission of hot or cold fluid, or a circuit for the circulation of hot or cold heat transfer fluid), and b) insulation on the portion of the catheter that is inserted to insulate the heat transmitting core from the portion of the patient""s body adjacent the insulation. The invention also relates to methods of use of such probes or catheters.
When a catheter or probe is inserted into a patient, it is generally desirable to have a catheter of the lowest possible diameter. If the probe or catheter is inserted into the body via an existing body orifice, such as the urethra or vagina, the acceptable diameter of the catheter is dictated by the diameter of the body orifice. On the other hand, if the probe or catheter is inserted into the body via a percutaneous puncture site or incision, as is the case in percutaneous vascular catheters or catheters inserted through a sheath or trocar during minimally invasive surgery, the acceptable diameter is dictated by the acceptable size of the percutaneous puncture site or incision. In such cases, a smaller puncture site or incision is generally preferable to a larger puncture site or incision.
In certain medical procedures, it is desirable to place a catheter into the body with a region that is at a different temperature than that of the surrounding body tissue. For example, in some medical procedures it is desirable to place a probe or catheter having a heat exchanger (e.g., a heatexchange surface or balloon) that is either hotter or colder than the surrounding blood, into a body lumen such as a blood vessel of a patient such that the heat exchanger will effect warming or cooling of either the blood flowing through the vessel or the tissues adjacent thereto such as the vessel wall.
Heat exchanging catheters may be used to exchange heat with the blood, for example, to remove heat from the blood to induce whole body or regional hypothermia for the purpose of treating, or minimizing the adverse effects of certain neurological diseases or disorders such as head trauma, spinal trauma and hemorrhagic or ischemic stroke. Additionally, it is sometimes desirable to induce whole body or regional hypothermia for the purpose of facilitating or minimizing adverse effects, such as neuronal damage, of certain surgical or interventional procedures such as open heart surgery, aneurysm repair surgeries, endovascular procedures, spinal surgeries, or other surgeries where blood flow to the brain, spinal cord or vital organs may be interrupted or compromised. Hypothermia has also been found to be advantageous to protect cardiac muscle tissue during and/or after myocardial ischemia and is protective of other tissues such as kidney or liver tissue.
Neural tissue such as the brain or spinal cord, is particularly subject to damage by vascular disease processes including, but not limited to ischemic or hemorrhagic stroke, blood deprivation for any reason including cardiac arrest, intracerebral or intracranial hemorrhage, and head trauma. In each of these instances, damage to brain tissue may occur because of brain ischemia, increased intracranial pressure, edema or other processes, often resulting in a loss of cerebral function and permanent neurological deficits. Likewise, during surgical procedures, it is often impossible to avoid disrupting the blood supply to all or part of the brain or spinal cord. This ischemia, even if very localized or very temporary, may nonetheless result in very serious and permanent injury to the patient.
Hypothermia applied to the neural tissue is known to be very neuroprotective. Although the exact mechanism for neuroprotection is not fully understood, lowering the brain temperature is believed to effect neuroprotection through several mechanisms including, the blunting of any elevation in the concentration of neurotransmitters (e.g., glutamate) occurring after ischemic insult, reduction of cerebral metabolic rate, reduction of intracranial pressure (ICP), moderation of intracellular calcium transport/metabolism, prevention of ischemia-induced inhibitions of intracellular protein synthesis and/or reduction of free radical formation as well as other enzymatic cascades and even genetic responses including apoptosis. Thus intentionally induced hypothermia of the neural tissue may prevent damage to brain or other neurological tissue during surgery or as a result of stroke, intracerebral hemorrhage and trauma.
The mammalian body generally functions most efficiently at normothermia. Therefore maintaining hypothermia in a portion of the body such as the brain or heart while maintaining the temperature of the rest of the body at normothermia may provide for protection of the target tissue, e.g. neuroprotection of the brain or protection of the myocardium from ischemic damage, while allowing the rest of the body to function at normothermia. Therefore a device that would facilitate the regional application of temperature exchange would be highly advantageous.
U.S. Pat. No. 5,486,208 (Ginsburg) describes an intravascular heat exchange catheter that comprises an elongate catheter shaft having a discrete heat transfer region located near its distal end. In one embodiment described in this patent, the catheter is inserted into a blood vessel of the patient and heat exchange fluid is circulated through the catheter shaft to the heat transfer region. By heating or cooling the heat transfer region, heat is transferred to or from the blood that flows through the vessel past the heat transfer region of the catheter. In this manner, the tissue perfused by the blood may be increased or decreased, as desired, including in some instances the entire body of the patient. Although the heat transfer is intended to occur at the discrete heat transfer region, the heated or cooled fluid is circulated through the catheter shaft proximal to the heat transfer region and no separate insulator is included to deter or prevent heat transfer from occurring between the proximal portion of the catheter shaft and the patient""s blood. Thus, even though the intended site of the heat transfer may be at the heat transfer region of the catheter, some unintended heat transfer could occur between the proximal catheter shaft and the patient""s blood, depending on the difference in temperature between the heat transfer fluid and the patients blood, as well as the construction of the proximal catheter shaft.
U.S. Pat. No. 5,624,392 (Saab) describes a heat transfer catheter apparatus that comprises very thin-walled, high strength thermoplastic tubular material defining a plurality of lumens. At least two of the lumens are adjacent to each other and readily inflatable under fluid pressure and readily collapsible under vacuum. Fluid connection means are provided at or proximate to the distal ends of the two adjacent lumens, to define a continuous loop fluid containment and circulation system. Heat transfer fluid from a first (inlet) lumen is passed directly to a second (outlet) lumen such that a continuous flow of heat transfer fluid through the two lumens can be established and maintained. Because no separate insulator is described as being formed on the exterior of the proximal portion of the Saab catheter, unintended temperature exchange could occur between the proximal catheter shaft and the patients blood, depending on the difference in temperature between the temperature exchange fluid and the patient""s blood, as well as the construction of the proximal catheter shaft.
Also, for example, U.S. Pat. No. 4,941,475 (Williams, et al.) describes a catheter that is useable to perform thermodilution cardiac output measurements. The thermodilution catheter described by Williams et al. comprises an elongate catheter shaft, a heat exchange balloon located on the catheter shaft, a lumen that extends from the proximal end of the catheter shaft to the heat exchange balloon, and a thermistor or sensor located distal to the balloon. A bolus of heated or cooled fluid is injected through the lumen and into the heat exchange balloon. Heat is thus added to or removed from the blood flowing past the heat exchange balloon and the thermistor or sensor is used to determine the rate of temperature change in the flowing blood. The patient""s cardiac output is then computed on the basis of the rate of temperature change of the flowing blood. Although the temperature exchange with the blood is intended to occur only at the location of the heat exchange balloon, no insulator is provided on the catheter shaft proximal to the heat exchange balloon and, thus, depending on the difference in temperature between the temperature exchange fluid and the patient""s blood, as well as the construction of the proximal catheter shaft, some unintended heat exchange could occur between the proximal catheter shaft and the patient s blood or tissue. The unintended heat transfer to the blood at locations other than at the heat exchange balloon would affect the temperature of the blood in general, with possible adverse effects. In addition, maintaining the temperature of the heat exchange fluid at a maximum difference from the blood temperature is helpful in decreasing the noise to signal ratio and increasing the accuracy of the blood flow determination using this thermodilution catheter. Preventing the loss of heat to the blood would be very helpful in accomplishing this goal.
The desirability of providing some insulation on the exterior of the proximal shaft of a heat exchange catheter is addressed by U.S. Pat. No. 5,257,977 (Eschel), which describes a trans-urethral catheter useable to thermally treat prostate tissue. The catheter comprises an elongate catheter shaft, a discrete temperature exchange region, lumens that extend through the catheter shaft for circulating of heated fluid through the temperature exchange region and an insulator formed about the catheter shaft proximal to the temperature exchange region. The insulator comprises a multiplicity of sealed enclosures that contain trapped gas to decrease heat exchange between the heated liquid that is being circulated through the catheter shaft proximal to the heat exchange region and the surrounding wall of the urethra. However, the insulator of the Eschel catheter has a fixed diameter and results in an increase in the diameter of the proximal catheter shaft of the Eschel device.
Given the above-described desirability of minimizing the diameter of the insertion profile of the shaft of heat exchange catheters and probes during their insertion and advancement through blood vessels or other body lumens, but a simultaneous need for maximum thermal insulation of a heat exchange catheter or probe shaft after the catheter or probe is in place within the body of a patient, there exists a need in the art for the development of improved means for insulating portions of those heat exchange catheters or probes without requiring enlargement of the diameter of the catheter or probe during its insertion and advancement.
The present invention provides a heat exchange probe or catheter that generally comprises a) an elongate shaft having a proximal end and a distal end and a thermally-transmissive core; b) at least one heat exchange region formed on the elongate shaft, said heat exchange region having a tissue-contacting heat exchange surface through which heat may be exchanged between the thermally transmissive core and the adjacent body tissue (e.g., blood that flows past the heat exchange region); and c) an insulator disposed on the elongate shaft proximal to the heat exchange region, such insulator being initially disposed in a radially collapsed configuration and subsequently moveable to a radially expanded configuration. When in its radially expanded configuration, the insulator is effective to insulate the shaft to prevent exchange of heat between the thermally conductive core underneath the insulator and the patients blood or body tissue adjacent the exterior of the insulator.
In accordance with the invention, the insulator may comprise one or more inflatable balloons or bladders disposed about the elongate shaft proximal to the heat exchange region. For example, a plurality of elongate balloons may be disposed generally parallel to the elongate shaft so as to substantially surround the shaft and act to center the shaft between them when they are inflated. Alternatively, the insulated region may comprise a single large balloon that surrounds the shaft. The balloon may be provided with flexible attachments or other tethers extending between the shaft surface and the interior wall of the insulation balloon so that, when the insulating balloon is fully expanded, those attachments or tethers will hold the shaft in the approximate center of the insulating balloon.
Further in accordance with the invention, the insulator may comprise any suitable material, but preferably will comprise an inflatable, thin walled material that is relatively non-compliant, that is, will expand to a predictable diameter and then will not expand further, even if greater inflation pressure is applied. One such suitable material is polyethylene terepthalate (PET). Blood compatible insulation fluids, such as carbon dioxide or helium may be used to inflate the inflatable insulator, after the catheter has been inserted and advanced to its desired position within the patient""s vasculature.
The heat exchange region of the catheter or probe may be formed on the elongate shaft. The thermally transmissive core of the elongate shaft may comprise one or more fluid circulation path(s) or lumen(s), whereby heated or cooled fluid may be passed into and/or extracted from the heat exchange region via the portion of the elongate shaft that is proximal to the heat exchange region. In embodiments where the thermally transmissive core comprises one or more fluid flow lumens, a heat exchange fluid may be circulated into or through the heat exchange region via such lumen(s).